With baby #1, I had an epidural 12 minutes before he was born. Immediately after it was administered, my blood pressure tanked, baby's heartrate dropped into the 60s, and chaos erupted in the room. The midwife was yelling to get the OR prepped, while checking me, finding me fully dilated, and placing a vacuum on our son's head. He yelled at me to "PUSH!", and he came out in just a few pushes. (His heart rate quickly recovered and he cried almost immediately.) A couple hours after birth, they had me get up to go the bathroom and I fainted because my BP was still so low. By 24 hours after the birth, I had developed a spinal headache because the anesthesiologist had nicked my spinal column during the procedure. I could not lift my head without crying from the pain. After putting up with that for another 24 hours (they have me percoset, but that did nothing), I went back to the hospital and got a blood patch. Twenty minutes later, I felt a thousand times better.
My experience is not typical, but dropping blood pressure happens around 20% of the time. Spinal headaches occur in 1-2% of epidurals.
Now, after all that, 11 hours into my Pitocin induction with baby #2, I still asked for an epidural. Fortunately, the anesthesiologist was wheeling his cart in right when I was saying, "I'm pushing!"
(I wised up with baby #3 and had him at home .)
As a doula, I rarely see moms get epidurals if they say they don't want one before labor begins. The only times I've seen them are 1) long labor and 2) inductions. (Even these aren't guarantees, of course: I've seen days-long labors and Pit inductions without epidurals as well.) If you don't want one, I'd recommend:
1. hire a doula
2. don't go to the hospital until you're in very active labor (and go home again if you go in and are 4 cm or less)
3. don't get induced (unless medically indicated -- then get a second opinion)
4. when you first go into labor, take a nap! (I like everyone else's suggestions, too, for keeping up energy and dealing with a super long labor)
5. consider chiropractic and/or info from spinningbabies.com to optimize baby's position before labor